In the past, many devices have been proposed for correcting operational errors for scales. Usually these devices include adding additional compensatory springs, such as may be seen in the patent to: Gerald C. Freeman; U.S. Pat. No. 3,807,517; issued Apr. 30, 1974.
Recently, there has been invented a scale whose leaf springs are automatically self-compensating for errors in the spring rate over the entire weighing range. Such a scale is shown in the U.S. Pat. No. 4,022,288 to Louis T. Canevari.
Although the latter invention eliminates the operational errors of the scale, there still exists inherent errors due to differences in manufacture, i.e. manufacturing tolerances which initially change the spring constant. For example, a manufacturing tolerance of .+-. 0.002 inches at 0.047 inch thickness in the thickness of the leaf springs is enough to affect the initial spring rate by 20%. The above tolerance is quite common, and therefore, ways have been devised to compensate for this type of distortion. One method is to place an adjustment spring of the type suggested in the aforementioned patent application. However, a different compensatory spring rate is needed for each scale, thus requiring an individual matching and testing of adjustment springs for each scale.
In order to eliminate this burdensome chore, the subject invention has conceived of an easily adjustable compensation spring. This compensation spring has an adjustable spring rate, that when added to the spring rate of the leaf springs will provide the desired spring constant for the scale system.